A power conversion controlling apparatus using an inverter is used very widely including application to AC motor generators from the motor control field to the generator control field, application to rectifier circuits and system interconnection inverters that exchange power between an AC power supply and a DC power supply, and the like. These usually have an electromotive force source in an AC circuit and the inverter must be controlled in synchronization with such an electromotive force source.
Thus, to make the inverter work, a switching control signal is generated based on phase information of an AC electromotive force source acquired by means of some sensor or phase information estimated based on the output voltage/current of the inverter and circuit constants of an AC circuit.
A typical electromotive load on the AC circuit side is a synchronous motor and a Hall device, an encoder, a resolver or the like is used as a magnetic pole position sensor to acquire the phase information of the electromotive force in inverter drive particularly of a permanent-magnet synchronous motor or a DC brushless motor. Control modes for detecting such magnetic pole position information can easily deal with high-efficiency operation and high-speed response control, but since a magnetic pole position sensor is needed, problems arise regarding reliability, workability, prices and the like.
On the other hand, various techniques have been proposed to indirectly control the position of rotor from information of the voltage and current of a motor by computation without using such a magnetic pole position sensor. For example, techniques based on detection of induced electromotive force of a motor by rectangular current drive, that based on detection of the voltage when a zero cross point of current in sinusoidal current drive is detected (for example, see Patent Document 1), that based on V/f constant control (for example, see Patent Document 2), and that with a vibration suppression function added to the V/f constant control (for example, see Patent Documents 3 and 4) have been proposed or practically used. However, though the position sensor can be eliminated, conventional control modes have problems that circuit constants of a motor must be incorporated into a control system, such conventional control modes are susceptible to transient changes, the control system will become more complicated, and the like.
Though an induction motor is also considered to be a load having the electromotive force, in comparison with the synchronous motor, the induction motor can be operated without detecting the phase information of the electromotive force and thus, speed control can be performed relatively easily by the V/f constant control and the like. However, the V/f constant control is not E/f constant control and thus, there are problems of lower torque and substantially of responsiveness during low-speed operation. Slip frequency control type vector control or the like is used to ensure fast responsiveness, but with the control system configured by incorporating circuit constants and integrating the induction motor and control device, there are problems that the system configuration will become more complicated and its response characteristics are affected by the circuit constants.
If, on the other hand, an AC generator or a commercial power supply is connected to the AC circuit side and an inverter is used to perform a rectification operation or an interconnected operation from a DC power supply to an AC system, a phase detector of a power supply voltage for generating a control signal in synchronization with the power supply voltage is generally needed. This leads, however, to lower reliability due to a more complicated control system caused by an additional need for an AC power supply voltage detector.
Though a control technique to make a rectification operation or an inversion operation perform by computation with the detected voltage and current of the inverter without using any phase detector of the power supply voltage is known, complicated computation processing is required due to the use of circuit constants (such as the impedance and magnetic flux density of a motor). Also, there is a problem that, for example, it is difficult to deal with wide variations in power supply frequency.
Patent Document 1: Japanese Patent Application Laid-Open No. H5-236789
Patent Document 2: Japanese Patent Application Laid-Open No. 2000-232800
Patent Document 3: Japanese Patent Application Laid-Open No. 2000-236694
Patent Document 4: Japanese Patent Application Laid-Open No. 2000-204694